1. Field of the Invention
The present invention relates to a semiconductor optical amplifier module.
2. Description of the Related Art
In the field of optical communications, to compensate transmission losses of optical fibers and insertion losses of optical components such as Arrayed Waveguide Grating (AWG) devices, it is very important to employ an optical amplifier having a low noise level and a high gain. In recent years, simple current pumping type semiconductor optical amplifiers (SOAs) have been drawing a lot of attentions because, unlike Erbium (Er)-Doped Fiber Amplifiers (EDFAs), current pumping type semiconductor optical amplifiers do not require a pump laser and are compact and inexpensive. Further, because semiconductor optical amplifiers are compact, it is possible to integrate a semiconductor optical amplifier with a silicon (Si) waveguide or a silica-based optical waveguide such as a Planar Lightwave Circuit (PLC) in a hybrid manner, while allowing the semiconductor optical amplifier to have the function of, for example, compensating waveguide losses and realizing optical switching (see, for example, T. Hashimoto et al., “Multichip Optical Hybrid Integration Technique with Planar Lightwave Circuit Platform”, J. Lightwave Technol., vol. 16, No. 7, pp. 1249-1258, July 1998). At the beginning of development, semiconductor optical amplifiers were found to be not as good as EDFAs in terms of saturation output characteristics thereof and Noise Figure (NF) characteristics thereof; however, as the development has advanced these days, it has been reported that semiconductor optical amplifiers that are comparable to EDFAs in terms of the saturation output characteristics thereof and the Noise Figure characteristics thereof are available (see, for example, K. Morito et al., “A Broad-Band MQW Semiconductor Optical Amplifier With High Saturation Output Power and Low Noise Figure”, IEEE Photonics Technol. Lett., vol. 17, No. 5, pp. 974-976, May 2005).
In an actual system, to employ a semiconductor optical amplifier, which is advantageous in terms of the size and the cost as described above, it is necessary to install the semiconductor optical amplifier on a module that is provided with a photo detector (PD) made of semiconductor or the like and being configured so as to monitor powers of optical inputs and outputs and in which an input unit and an output unit are connected to optical fibers.